The present invention relates to a process and apparatus for forming single-sided, double-sided, or multi-layer circuit boards.
The manufacture of printed circuit boards generally follows either subtractive or additive processing techniques. According to a general subtractive process for the manufacture of printed circuit boards, a conductive layer laminated to a non-conductive substrate is selectively removed to leave a desired pattern of conductive pathways. The pattern of conductive pathways is typically formed by providing the conductive layer with a resist film, for example containing photosensitive organic monomers. Upon exposure to ultraviolet light, the photosensitive organic monomers polymerize, forming hardened regions. Two types of resists are in common usage today: dry film resists, containing a thin film of photosensitive monomers covered by a ultraviolet-transparent protective film, and liquid resists, also containing photosensitive organic monomers, often present in a solution allowing application as a liquid.
Once the resist has been applied to the conductive layer, the resist is photo-imaged, i.e., selectively exposed to an appropriate ultraviolet light source. An imaging mask is interposed between the source of ultraviolet light and the circuit board containing the resist. The imaging mask includes an ultraviolet-opaque member having an ultraviolet-transparent pattern therein. Accordingly, when the circuit board is photo-imaged only those regions corresponding to the ultraviolet-transparent pattern will be exposed and polymerized.
Subsequent to imaging, the unexposed, and therefore un-polymerized regions of the resist are removed, as through the use of appropriate solvents. The regions of the conductive layer not protected by the polymerized resist are then removed using an acid or alkaline solution. Once the resist has been removed, the non-conductive substrate is left containing the conductive layer in the pattern corresponding to ultraviolet-transparent pattern of the imaging mask.
Additive processes for the manufacture of printed circuit boards typically begin with a non-conductive substrate upon which conductive pathways are selectively added. Consistent with a conventional additive process, a non-conductive substrate containing a resist layer, such as those employed during subtractive methods. The substrate bearing the resist layer is imaged with a negative photo-resist, wherein only those regions corresponding to the desired pattern of conductive pathways remains unexposed. Accordingly, when the resist is developed, i.e., the un-polymerized resist is removed, the non-conductive substrate is exposed in the regions corresponding to the desired conductive pathways. Plating the exposed portions of the non-conductive substrate with a conductive material, and then removing the polymerized regions of the resist completes the process.
A process for forming a printed circuit including correcting the inherent positional errors of a printer, using the corrected printer to print an etch resist mask directly onto a conductive layer of the circuit board, and then removing the regions of the conductive layer that are not covered by the etch resist mask. The positional errors of the printer are corrected by first ascertaining the positional errors of the printer. This may be accomplished by printing a test pattern that is representative of a known standard pattern. The printed test pattern may then be compared with the known standard pattern in order to determine any deviation of the printed test pattern from the standard pattern. Printer inputs may then be manipulated to compensate for the ascertained errors, whereby printed patterns overcome the inherent errors of the printer. Advantageously, error correction of the printer also includes the use of servomechanisms to control the feed of the substrate through the printer, as well as for triggering print initiation.
Once the printer has been corrected to overcome inherent positional errors, the printer is used to print and etch resist pattern mask directly onto a conductive layer that is disposed on a printed circuit substrate. The pattern mask printed directly onto the conductive layer may correspond to a desired pattern of conductive pathways in the printed circuit. Subsequently, any regions of the conductive layer not protected by the etch resist pattern mask may be removed from the substrate, as by an etching process.
According to another aspect, an error corrected printer may be used to print a plating resist mask directly onto a portion of a printed circuit substrate. A conductive material may then be applied to those regions of the printed circuit substrate not protected by the plating resist mask. Thereafter, the plating resist mask may be removed from the printed circuit substrate, along with any conductive material not corresponding to those regions of the printed circuit exposed by the plating resist mask.
The invention herein is also applicable to forming two-sided printed circuit boards, both by etching and by plating. A two-sided printed circuit may be formed consistent with the present invention by respectively printing either an etch resist pattern mask, or a plating resist pattern mask to a second side of the printed circuit substrate. Desirably, a printed circuit formed on a second side of the substrate is also formed by printing the pattern mask using an error corrected printer.
The process of the invention herein may also be used to fabricate multiplayer laminate printed circuit boards. Individually formed printed circuit boards, either single sided or double sided, may be laminated into a composite structure, wherein the individual printed circuits are generally isolated one from another by interleaved insulating layers.
Furthermore, the present invention relates to a method of printing a pattern mask and/or a pattern of conductors directly to a substrate, such as an etch resist mask applied to a conductive layer on a substrate or a plating mask applied to a surface of substrate. The method consistent with the present invention includes printing a first pattern mask to the substrate, or a conductive layer disposed thereon, using a printer that has been corrected for inherent positional errors. Subsequent to printing the first pattern mask, the position and/or orientation of the first pattern mask is detected. Alternatively, the substrate may be held in a fixed orientation on a substrate feed system, whereby the position and orientation of the first pattern mask is prevented from shifting from a known position. The position and orientation of the first pattern mask may be know by the fixed orientation of the substrate, or may be detected using such techniques as optical scanning or laser scanning the surface of the substrate in order to determine the precise placement and orientation of the first pattern mask. Based on the detected position and/or orientation of the first pattern mask, a second pattern mask or conductor is printed onto the substrate. The second pattern mask may be printed in register with the first pattern mask, or in complimentary manner relative to the first pattern mask. Consistent with this method, the second pattern mask may be precisely positioned on the substrate in order to accommodate any positional and/or orientation errors that may have occurred during the printing of the first pattern mask.